5. Chewie And R2 Are Rebel Spies - Star Wars
The Crazy Theory: C-3PO may get his memory wiped at the end of Revenge Of The Sith, but that only deals with one character in an entire posse who know the whole Anakin is Vader shebang. This creates some rather stark plot discrepancies between the prequels and the originals; why didn't R2 explain the truth to Luke and how come Chewie never so much a growled recognition of the Jedi? Because they're secretly rebel spies!
Why It Cant Be True: Good God this theory has a lot of traction. Look at any list of fan theories and thisll pop up at some point, which has always thrown me. Its such a bland idea that I think it only exists because it was easier than admitting Lucas didn't watch his classic trilogy before making the new one. The problem is that in R2s case its not really a theory - hes worked with the Rebels for decades so probably is privy to many things (and good at keeping schtum) - and with Chewie its too contrived to be taken seriously. I guess its just too close to the accepted continuity (obviously they were keeping quiet for security reasons) that it feels like unnecessary embellishment. Its a theory created to solve a problem that can really be sorted in without it.